Pottery Glaze Colorant Calculator

Cobalt oxide is one of the strongest tinting colorants used in ceramics, so very small amounts produce strong color. A light blue typically needs about 0.25 to 0.5 percent cobalt oxide by weight of the base glaze, a medium blue needs roughly 1 percent, and a strong, saturated blue needs 1.5 to 2 percent. Cobalt carbonate gives a softer, less spotty distribution than cobalt oxide and is often preferred for brushed or hand-applied work.

Oxides and carbonates of the same metal produce similar final colors after firing, but carbonates typically have a finer, more uniform particle size, which distributes more smoothly through the glaze and reduces speckling or color concentration spots. Carbonates also tend to be slightly less concentrated by weight than the pure oxide, so recipes calling for carbonate forms often use a percentage at the higher end of the typical range.

Copper is highly sensitive to kiln atmosphere. In an oxidation firing, where plenty of oxygen is present, copper produces green to turquoise colors. In a reduction firing, where oxygen is limited and the kiln atmosphere is starved, copper produces the famous copper red ("sang de boeuf") effect. The same copper oxide percentage can yield dramatically different results depending entirely on whether the kiln is firing in oxidation or reduction.

Yes, and many classic glaze colors are blends rather than single oxides. Black glazes commonly combine iron oxide, cobalt carbonate, and manganese dioxide. Purple and aubergine tones often combine manganese with a small amount of cobalt. When blending colorants, introduce them at conservative percentages first and test on tiles, since colorant interactions are not always additive and can shift hue unexpectedly.

Several common colorants, including cobalt, nickel, chrome, and manganese compounds, are classified with higher toxicity and require careful handling: wear a NIOSH-rated dust mask when weighing dry materials, avoid skin contact, and work in a ventilated area. Iron oxide, rutile, tin oxide, and zircon-based opacifiers carry lower toxicity but should still be handled with basic dust precautions, since inhaling any fine ceramic powder repeatedly is harmful.

Chrome oxide reacts with tin oxide at firing temperature to produce a pink to red color known as chrome-tin pink, even when only trace amounts of chrome are present from kiln contamination. If you use chrome green glazes and tin-opacified white glazes in the same studio, keep dedicated equipment, brushes, and glazing areas for each to avoid unwanted color shifts from cross-contamination.

Mason stains are pre-calcined, pre-fritted colorant blends manufactured for color consistency and stability. They typically require a higher percentage, around 3 to 10 percent, than the equivalent raw oxide, but they produce far more predictable, repeatable color from batch to batch and kiln to kiln. Raw oxides are less expensive and give a wider range of natural variation, which many studio potters value for one-of-a-kind work.